Smart cards hold data for using services, such as prepaid telephone call charge units, for example. ISO Standard 7810 imposes strict constraints and specifications on the size, mechanical strength and reliability of these electronic cards. One important aspect is the mechanical strength of the card, i.e. its ability to withstand the stresses to which it is subjected and which may damage it, to the extent of ripping out the integrated circuit chip, for example.
Manufacturing the cards is made all the more difficult by their small size, especially their thickness (0.8 mm).
One of the major problems with manufacturing smart cards is fastening the module to the card body.
Prior art cards are molded, as described in the applicant's U.S. Pat. No. 5,164,144, for example, using a mold having a hollow space defining the exterior shape of the card body and delimited by two main walls corresponding to the two major sides of the card. In this implementation, the smart cards comprise three components, namely a card body, a support member having a graphic on at least one side and an electronic module. A support member having a graphic on at least one side is placed in said mold and held against a first wall of the hollow space. A thermoplastic material is injected into the mold to fill all of the volume delimited by the hollow space not occupied by the support member. The card body with the support member carrying the graphic attached to it is then removed from the mold.
A recess is formed on the opposite major side of the card body to that carrying the support member to enable insertion of the electronic module when molding the card body. The shape of the recess is complementary to that of the electronic module.
The electronic module is inserted and fixed to the card body by a prior art method such as that disclosed in U.S. Pat. No. 4,737,620, for example. This document discloses a process in which pegs or projections in the recess receiving the electronic module are heated to a temperature at which they soften and the module is pressed down to flatten the tips of the pegs or projections until the module reaches the correct position, i.e. until the contact arrays are substantially coplanar with the respective major side of the card body. Fastening of the module to the card body is completed by injecting an insulative adhesive between the back of the recess and the electronic module.
Another prior art method for inserting and fixing an electronic module into a smart card is described in U.S. Pat. No. 4,625,102. In this prior art method, the electronic module is placed on a flat-ended tool associated with heating means. The module is pressed into the correct position due to the combined effect of pressure and localized heating. The plastics material of the card body flows when the electronic module is pressed in and fills a hole through the module with a flared end whereby the material filling the hole acts as rivets.
Published European patent application No. 449691 discloses a method of fixing an electronic module to a card body in which a stamping tool with multiple spikes is dipped into a container of adhesive so that droplets of the adhesive form at the ends of the spikes and are transferred to the card body when the tool is applied to it. The cavity receiving the electronic module is staggered in the sense that it has a smaller lower housing and a larger upper housing opening onto the upper surface of the card body. The edge of the bottom of the upper housing therefore forms a shoulder parallel to the upper surface of the card body. The droplets of adhesive are deposited onto this shoulder. When the spiked tool is applied to this shoulder the droplets at the ends of the spikes remain on the surface of the shoulder 20 because of the different surface tensions of the materials of the spikes and the card body. The next step is to place the electronic module in the cavity and to polymerise the adhesive. In this well-known process, the adhesive is preferably a cyano-acrylate adhesive.
These prior art methods are satisfactory for fixing the graphic support member to the card body. However, they are open to improvement in respect of fitting the electronic module and fastening it to the card body.
In the above-described approaches, the support member and the electronic module are fitted to the card body in two separate and successive operations. Also, fitting the module by virtue of partial softening of the card body is relatively difficult. Furthermore, adhesives and resins like epoxy resin used to fix the electronic module to the card body are subject to shrinkage, admittedly slight but nevertheless sufficient to compromise the relative positions of the module and the card body. If the electronic module is fitted by one of the prior art methods it can be removed from the card body and fixed to another. The method of the present invention is such that the module cannot be removed without destroying it.